It has heretofore been suggested that the valves of a hydraulic transmission such as utilized in vehicles can be controlled by a microprocessor which includes sensors that sense variables such as road speed, throttle position and engine rpm and functions to provide pulses to pulse width modulated valves which in turn control spool valves for operating clutches in the transmission or control clutches directly.
In such pulse width modulator valves, it is desirable to be able to accurately control the pressure of the fluid.
The space requirements are quite small and therefore require a small valve which will function effectively in a pulse width modulated mode to provide the fluid at constant pressure.
Accordingly, among the objectives of the present invention are to provide a solenoid valve which is small, utilizes a minimum number of parts to produce the desired control of pressure and can be used in a pulse width modulated mode or in a steady state directional mode.
In accordance with the invention, the pulse width modulated valve comprises a valve housing including a transverse wall, an integral extension extending axially from the transverse wall and an integral peripheral wall extending axially from the periphery of the transverse wall in a direction opposite to the direction in which the axial extension extends. The solenoid valve also includes a pole member including a pole piece extending axially inwardly of the housing, an integral transverse wall extending radially outwardly into engagement with the peripheral wall and connected thereto. The pole piece has an axial passage therethrough and defines a first conical seat. The axial extension of the housing has an axial passage aligned with the opening of the pole, an insert is positioned in the axial passage in the axial extension and defines a second seat. A ball is interposed between the first and second seats and has limited movement between the seats. A spring means yieldingly urges the ball into engagement with the second seat. The insert has portions thereof spaced from the walls of the passage into which the insert extends defining passages to the exterior of the axial extension. The housing and pole member define an annular space and a coil assembly is positioned in the annular space, such that when fluid is applied to the axial passage in the insert and the coil is de-energized, the spring means holds the ball against the second seat and prevents flow through the axial passage in the insert while permitting communication between the passages defined by the insert about the ball and first seat through the axial passage in the pole and when the solenoid is energized, the ball is drawn toward the first seat to close communication to the axial opening in the pole and permit flow from the axial passage in the insert past the second seat through the passages defined by the insert to the exterior of the axial extension.